[Tropical] Tropical Cyclone Discussion

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WTNT45 KNHC 082058
TCDAT5

TROPICAL STORM NATE DISCUSSION NUMBER   5
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL152011
400 PM CDT THU SEP 08 2011

ALTHOUGH THE SATELLITE APPEARANCE OF NATE HAS NOT CHANGED MUCH
THIS AFTERNOON...AN AIR FORCE RESERVE HURRICANE HUNTER AIRCRAFT
HAS REPORTED PEAK 1000-FT FLIGHT-LEVEL WINDS OF 81 KT AND BELIEVABLE
SFMR SURFACE WINDS OF AROUND 60 KT.  BASED ON THESE DATA...THE
INITIAL INTENSITY IS INCREASED TO 60 KT.  THE CENTER REMAINS NEAR
THE NORTHEASTERN EDGE OF THE DEEP CONVECTION DUE TO LIGHT TO
MODERATE NORTHEASTERLY SHEAR.  THE SHEAR IS EXPECTED TO WEAKEN
DURING THE NEXT 12-24 HOURS...WHICH SHOULD PLACE NATE IN A
FAVORABLE ENVIRONMENT FOR STRENGTHENING DURING THE NEXT FEW DAYS.
THE UPDATED INTENSITY FORECAST IS ABOVE THE PREVIOUS ADVISORY AND IS
A BLEND OF THE SHIPS/LGEM GUIDANCE.

FIXES FROM THE AIRCRAFT SHOW THAT NATE HAS MOVED SLOWLY
SOUTH-SOUTHEASTWARD DURING THE PAST 24 HOURS.  THE INITIAL MOTION
ESTIMATE IS 160/2 KT.  THE OVERALL FORECAST REASONING HAS CHANGED
LITTLE SINCE THIS MORNING.  NATE WILL REMAIN IN WEAK STEERING
CURRENTS DURING THE NEXT DAY OR SO...THEN IT SHOULD BEGIN MOVING
NORTHWARD AROUND THE WESTERN SIDE OF THE CARIBBEAN RIDGE.  AFTER
36-48 HOURS...THERE REMAINS A VERY LARGE SPREAD IN THE GUIDANCE...
HOWEVER THE MODELS HAVE GENERALLY SHIFTED WESTWARD.  THE GFS IS
ALONG THE EASTERN EDGE OF THE ENVELOPE AND SHOWS A SLOW NORTHWARD TO
NORTH-NORTHWESTWARD MOTION OVER THE CENTRAL GULF OF MEXICO.  MOST OF
THE REMAINDER OF THE TRACK MODELS MOVE NATE MORE WESTWARD TOWARD
MEXICO.  THE OFFICIAL FORECAST HAS BEEN SHIFTED TO THE LEFT...BUT
NOT NEARLY AS FAR WEST AS THE MULTI-MODEL CONSENSUS...OUT OF RESPECT
FOR THE GFS AND THE EARLIER ECMWF ENSEMBLE MEMBERS.


FORECAST POSITIONS AND MAX WINDS

INIT  08/2100Z 19.7N  92.3W   60 KT  70 MPH
 12H  09/0600Z 19.7N  92.2W   65 KT  75 MPH
 24H  09/1800Z 20.2N  92.3W   70 KT  80 MPH
 36H  10/0600Z 20.9N  92.8W   75 KT  85 MPH
 48H  10/1800Z 21.6N  93.3W   80 KT  90 MPH
 72H  11/1800Z 22.5N  94.0W   85 KT 100 MPH
 96H  12/1800Z 23.0N  94.5W   85 KT 100 MPH
120H  13/1800Z 23.5N  95.0W   85 KT 100 MPH

$$
FORECASTER BROWN



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